In a conventional optical receiver, monitoring an input optical power of an avalanche photodiode (APD) involves measuring a photocurrent flowing past the APD (Iapd) using a current monitoring controller chip. Namely, the current monitoring controller chip outputs a mirror current Iapd1 of the photocurrent Iapd, and then an analog-to-digital converter (ADC) samples and converts the mirror current Iapd1 into a digital signal ADC_Iapd representative of the analog current Iapd1. In embodiments wherein various input optical power values are received, various photocurrent values of Iapd are provided to the APD and subsequently converted to digital form (e.g., a current ADC_Iapd). The digital values of Iapd, ADC_Iapd, can then be utilized to form a current v. power graph, wherein the sampled ADC values of Iapd are plotted as the horizontal coordinates, and corresponding optical powers are plotted (in μW) as vertical coordinates. Based on this curve/graph, the least squares method can be used to obtain parameters a, b, c, d, and e of the following quadratic polynomial: Pinput (μW)=(a*ADC_Iapd4)+(b*ADC_Iapd3)+(c*ADC_Iapd2)+(d*ADC_Iapd)+e. If a real-time current value ADC_Iapd is obtained via sampling, it can obtain an input optical power value by entering the ADC_Iapdvalue into the above-mentioned equation. However, this mode is only compatible with the monitoring of continuous optical power signals.
Furthermore, since APDs are sensitive to bias voltage Vapd and ambient temperature, different APDs produce various photocurrents Iapd at the same input optical power, but with different bias voltages Vapd. Also, different APDs produce various photocurrents Iapd at the same bias voltage Vapd and input optical power, but at different temperatures. Therefore, conventional ways of monitoring the APD input optical power may have low precision, with an error control between ±3 dB.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.